【计算机图形学】裁剪算法（Cohen-Sutherland算法 & 中值分割算法 & Liang-Barsky算法）

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// 程序名称：中值裁剪

// 功 能：用中值分割算法实现直线段裁剪

// 编译环境：VS2019，EasyX_20220116

// 最后修改：2022-3-26

// Special Thanks To Gong WH

#include

#include

#include

using namespace std;

#define LEFT 1

#define RIGHT 2

#define BOTTOM 4

#define TOP 8

int XL, XR, YB, YT;

//区域编码

int encode(float x, float y, int* code) {

int c = 0;

if (x < XL) {

c = c | LEFT;

}

else if (x > XR) {

c = c | RIGHT;

}

if (y < YB) {

c = c | BOTTOM;;

}

else if (y > YT) {

c = c | TOP;

}

*code = c;

return 0;

}

void MidClip(float x1, float y1, float x2, float y2) {

int code1, code2;

encode(x1, y1, &code1);

encode(x2, y2, &code2);

//无法继续二分

if (abs(x1 - x2) + abs(y1 - y2) <= 2) {

return;

}

//线段完全不可见

if ((code1 & code2) != 0) {

return;

}

//线段完全可见

if ((code1 | code2) == 0) {

setlinecolor(WHITE);

line(x1, y1, x2, y2);

return;

}

//线段部分可见=>递归吧。。

int midx = (x1 + x2) / 2, midy = (y1 + y2) / 2;

MidClip(midx, midy, x2, y2);

MidClip(x1, y1, midx, midy);

/*

//这个优化，不大行

int midcode;

encode(midx, midy, &midcode);

//中点可见，继续二分

if (midcode == 0) {

MidClip(midx, midy, x2, y2);

MidClip(x1, y1, midx, midy);

}

//中点不可见，判断中点和哪个点在同一区域

else {

int cnt1[4] = { 0 }, cnt2[4] = { 0 }, cntmid[4] = { 0 };

//handle midcode

do {

if (midcode >= 8) {

cntmid[0] = 1;

midcode -= 8;

}

else if (midcode >= 4) {

cntmid[1] = 1;

midcode -= 4;

}

else if (midcode >= 2) {

cntmid[2] = 1;

midcode -= 2;

}

else if (midcode >= 1) {

cntmid[3] = 1;

midcode -= 1;

}

else {

continue;

}

} while (midcode != 0);

//handle code1

do {

if (code1 >= 8) {

cnt1[0] = 1;

code1 -= 8;

}

else if (code1 >= 4) {

cnt1[1] = 1;

code1 -= 4;

}

else if (code1 >= 2) {

cnt1[2] = 1;

code1 -= 2;

}

else if (code1 >= 1) {

cnt1[3] = 1;

code1 -= 1;

}

else {

continue;

}

} while (code1 != 0);

//handle code2

do {

if (code2 >= 8) {

cnt2[0] = 1;

code2 -= 8;

}

else if (code2 >= 4) {

cnt2[1] = 1;

code2 -= 4;

}

else if (code2 >= 2) {

cnt2[2] = 1;

code2 -= 2;

}

else if (code2 >= 1) {

cnt2[3] = 1;

code2 -= 1;

}

else {

continue;

}

} while (code2 != 0);

int count1 = 0, count2 = 0;

for (int i = 0; i < 4; i++) {

if (cnt1[i] == cntmid[i]) {

count1++;

}

if (cnt2[i] == cntmid[i]) {

count2++;

}

}

if (count1 > count2) {

//point 1 area is closer to midpoint area

MidClip(x1, y1, midx, midy);

}

else {

//point 2 area is closer to midpoint area

MidClip(midx, midy, x2, y2);

}

}

*/

}

int main() {

//用户定义a、b坐标

int xa, ya, xb, yb;

cout << "please input the coordinate of A point:" << endl;

cin >> xa >> ya;

cout << "please input the coordinate of B point:" << endl;

cin >> xb >> yb;

int x0, y0, x1, y1;

//0->left bottom; 1->right top;

//图形界面

initgraph(640, 480);

ExMessage m;

//勾勒AB线段：绿色

setlinecolor(GREEN);

line(xa, ya, xb, yb);

while (true) {

m = getmessage(EX_MOUSE | EX_KEY);

switch (m.message) {

case WM_LBUTTONDOWN:

x0 = m.x;

y0 = m.y;

setlinecolor(WHITE);

setfillcolor(GREEN);

fillrectangle(m.x - 3, m.y - 3, m.x + 3, m.y + 3);

case WM_RBUTTONDOWN:

x1 = m.x;

y1 = m.y;

setlinecolor(WHITE);

setfillcolor(GREEN);

fillrectangle(m.x - 3, m.y - 3, m.x + 3, m.y + 3);

//判断用户是左上~右下 / 左下~右上 / 右上~左下 / 右下~左上

if ((x0 < x1) && (y0 > y1)) {

XL = x0;

XR = x1;

YB = y1;

YT = y0;

}

else if ((x0 < x1) && (y0 < y1)) {

XL = x0;

XR = x1;

YB = y0;

YT = y1;

}

else if ((x0 > x1) && (y0 > y1)) {

XL = x1;

XR = x0;

YB = y1;

YT = y0;

}

else if ((x0 > x1) && (y0 < y1)) {

XL = x1;

XR = x0;

YB = y0;

YT = y1;

}

//勾勒裁剪框

setlinecolor(RED);

line(XL, YT, XR, YT);

line(XL, YB, XR, YB);

line(XL, YT, XL, YB);

line(XR, YT, XR, YB);

//裁剪部分为白色

MidClip(xa, ya, xb, yb);

case WM_KEYDOWN:

if (m.vkcode == VK_ESCAPE)

return 0; // 按 ESC 键退出程序

}

}

closegraph();

return 0;

}